The overall performance of high speed electronic systems operating in the multi-gigabit per second range is ultimately dependant on the signal integrity of the transmitted data. The first steps in controlling signal integrity are made in the design of the circuit. Choices made in terms of circuit layout, the materials used and the general architecture of the complete assembly will all have impact on the quality of the transmitted electronic signal. One of the major concerns in maintaining signal integrity is to assure that the signal encounters as few parasitic effects and electrical discontinuities as possible. One solution would be to have all signals in an electronic system be made by means of coaxial cable connections to provide and maintain a fully shielded conductor path having unvarying characteristic impedance through its entire path. However, this solution is impractical and too expensive for most electronic products.
In place of coaxial cables, microstrip and stripline interconnection paths are constructed to control the impedance and provide a measure of shielding. While these solutions have worked well for the industry for some years, as the electronics industry transitions into the gigahertz frequency due to the continuing advance of semiconductors processing, the old methods must be either replaced with new ones or the old methods must be modified to accommodate the changes needed. This is especially true as signals from the IC chip start out at a very fine pitch (i.e. circuit or contact width and spacing) and must from there graduate to the coarser pitches required for next level assembly. These transitions are normally characterized by junctions that are abrupt as the signal moves from one part of the interconnection chain to the next and, depending on the speed of the signal, these transitions can have profound effects on the signal integrity, manifest in the form of reflections and ringing in the circuit. Thus as circuit speeds climb, there is need for new approaches to design of interconnections from the chip through the interconnection chain, which will provide relief from those current design features and elements that degrade circuit performance.